1. Field of the Invention
The present invention relates to a communications system for communicating over the horizon, and more particularly to such a system which employs an acoustic source for providing variations in the density of the atmosphere above the source against which, or between which, the signal may be directed over the horizon.
2. Description of the Prior Art
In the prior art systems have been employed to stimulate the atmosphere to create changes in the index of refraction off of which signals may be reflected. Russian Patent SU1252749 A1 discloses the use of an acoustic impulse with a sinusoidal filling emitted vertically upward, and a transceiver which irradiates the acoustic impulse with an electromagnetic emission. The echo signal reflected from the wave is detected, to calculate the horizontal and vertical components of wind speed. This is not an over the horizon type of application.
U.S. Pat. No. 4,222,265, Ravussin, discloses an apparatus for automatically measuring the vertical profile of the temperature in the atmosphere by the measurement of the propagation speed of sound wave pulses to which it is directly related by means of a continuous Doppler radar. Again, no over the horizon feature is disclosed.
U.S. Pat. No. 4,761,650, Masuda et al., discloses a similar system for measuring wind velocity and temperature. A similar system is disclosed in an article "Acoustic Radar Reads Wind Speed Remotely" in the Dec. 22, 1961 issue of Electronics, page 16, wherein again the Doppler shift to the radar wave reflected from the acoustic wave is used to calculate the wind speed.
Prior art over the horizon radar and communications systems have employed the difference in density at the ionosphere, reflecting the radio wave off the ionosphere.
It is accordingly an object of the present invention to provide an over the horizon communications system utilizing acoustic variations set up in the atmosphere for redirecting a communications signal over the horizon.
It is another object of the invention to provide a radar over the horizon system in which the acoustic variations are used to reflect a radar wave going and coming.
It is still another object of the present invention to provide a communications system in which the communications signal is channeled between density variations set up by such an acoustic source.